This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP00/06026(not published in English) filed Sep. 6, 2000.
The present invention relates to an optical time domain reflectometer (hereinafter abbreviated to OTDR) and, more particularly to, an OTDR for injecting a light pulse to an optical fiber line under test and then receiving a return light therefrom to thereby measure transmission properties of the optical fiber line, the OTDR employing technologies for facilitating the evaluation of the optical fiber line.
An OTDR has conventionally been used to check for a fault or deterioration of an optical fiber line.
This type of OTDR injects a light pulse having the same wavelength as that of a light used by a communication system using an optical fiber line to one end of the optical fiber line under test so that until a predetermined time elapses from a time of that injection it can detect the intensity of the light reflected back to that end.
Then, the OTDR can display a waveform indicating a time-wise change (which can be calculated as a distance) in the intensity of that reflected light on the screen of a display, thus observing the transmission properties of the optical fiber line.
Recently, however, there has appeared a communication system for using an optical fiber line to multiple-transmit lights having different wavelengths.
To test such a communication system""s optical fiber line, the prior art has employed such a scheme that the OTDR side can selectively inject light pulses with different wavelengths to the optical fiber line and also that the final controlling element can be operated to switch these wavelength of the light pulses incident upon the optical fiber line in order to obtain waveform data for each of thus switched wavelength, thereby selectively displaying thus obtained waveform data for each wavelength by the operations of the final controlling element.
The above-mentioned prior art OTDR, however, has had to switch the wavelength by the operations of the final controlling element, thus leading to a problem of troublesome operations.
The above-mentioned prior art OTDR has had also to observe the waveform by sequentially switching the waveform data for each wavelength on the final controlling element, thus leading to a problem of difficulty in grasping a difference, due to a difference in wavelength, in the characteristics of the optical fiber line.
The above-mentioned prior art OTDR has also calculated characteristic values of the optical fiber at a plurality of event occurrence points on the optical fiber line and then displayed them in a list on an indicator (e.g., CRT, LCD, etc.), which has the following problem.
That is, the user of the OTDR has to localize a faulty one of the plurality of event occurrence points which has an abnormal value by visually inspecting the characteristic values displayed on the indicator, thus taking a considerably lapse of time to evaluate the optical fiber line.
IT is an object of the invention to provide an OTDR that solves the above-mentioned problems and that is easy in operation to facilitate grasping of a difference in characteristics of an optical fiber line caused by a difference in wavelength and also to discriminate, by displaying, characteristic values of event occurrence points on the optical fiber line between characteristic values outside an allowable range predetermined by the user and the other characteristic values, thus rapidly localizing the faulty points on the fiber line.
According to one aspect of the invention, there is provided an OTDR comprising:
a light pulse generating means (24) connected to one end of an optical fiber to be measured, for selectively injecting light pulses having a plurality of wavelengths to the optical fiber to be measured;
a light receiving means (30) for receiving the light reflected from the above-mentioned optical fiber to be measured to then output a signal corresponding to the intensity of that light received;
a memory means (32) for storing the signal output from the above-mentioned light receiving means as waveform data and then store it for each of the above-mentioned wavelengths;
an arithmetic operation means (40) for operating the positions and characteristics of the events based on the waveform data for each wavelength stored in the above-mentioned memory means;
a display unit (22) having a first and second display regions; and
display control means (41 and 46) for discriminating, by displaying in the first display region of the above-mentioned display unit, the waveform data pieces for each wavelength stored in the above-mentioned memory means from each other and, at the same time, displaying in the second display region of the second display region of the above-mentioned display unit the positions and characteristics of the events corresponding to each wavelength which are operated by the above-mentioned arithmetic operation means.